1. Field of the Invention
This invention relates to combinations of herbicides used for postemergent control of a broad spectrum of weeds. It also relates to a method of preparing and methods of using such combinations.
2. Description of Related Art
N-(Phosphonomethyl)glycine, also known by its common name glyphosate, is a widely-used broad spectrum postemergent herbicide used to control the growth and proliferation of undesired plants. In its acid form and its various salt forms, glyphosate is highly effective and commercially important for controlling weeds in agricultural, industrial, and residential markets. Typically it is applied to the foliage of the target plant, whereafter it is absorbed by the foliar tissue and translocated throughout the plant. N-(Phosphonomethyl)glycine noncompetitively blocks an important biochemical pathway which is common to virtually all plants, but which is absent in animals. Because of the nature of the biochemical pathway, visual symptoms that a plant has been treated with N-(phosphonomethyl)glycine may not appear until two weeks or more after treatment.
Various forms of N-(phosphonomethyl)glycine have been found to be commercially useful. It is sold and used in its acid form, or in a salt form. N-(Phosphonomethyl)glycine salts which are frequently used to control weeds include mono(isopropylammonium) N-(phosphonomethyl)glycine, monoammonium N-(phosphonomethyl)glycine, monosodium N-(phosphonomethyl)glycine, and monotrimethylsulfonium N-(phosphonomethyl)glycine. However, the range of N-(phosphonomethyl)glycine salts useful for controlling weeds is very broad (J. E. Franz et al., Glyphosate: A Unique Global Herbicide, ACS Monograph 189, American Chemical Society, Washington, D.C., 1997, pp. 27-64, herein incorporated by reference).
Numerous studies have been made on the effect of surfactants on the herbicidal action of N-(phosphonomethyl)glycine. Franz et al., pp. 155-161 (herein incorporated by reference) describe in detail the effects of many different surfactants and different classes of surfactants on N-(phosphonomethyl)glycine activity. N-(Phosphonomethyl)glycine has been formulated in a variety of ways, including a liquid, a water soluble granule, and a wettable powder.
Protoporphyrinogen oxidase inhibitor (PPO) herbicides are known to affect plants by inhibiting protoporphyrinogen oxidase in chloroplasts, thereby damaging photosynthesis and other processes. This damage causes early symptoms of tissue necrosis in plants. Some PPO herbicides such as the triazolinones (see, for example, U.S. Pat. No. 5,217,520, herein incorporated by reference) provide good control of broadleaf weeds but are less efficacious in controlling grasses.
Japanese Patent Application Publication Kokai Hei 10-45516 (herein incorporated by reference) describes a composition comprising N-(phosphonomethyl)glycine and a PPO herbicide known as carfentrazone. Carfentrazone is a high-melting solid carboxylic acid useful for postemergent control primarily of broadleaf weeds (U.S. Pat. No. 5,217,520, herein incorporated by reference).